The electrical power delivered by a solar panel depends in particular on its surface area and on the angle of incidence of the solar radiation on the panel. The efficiency per unit area of a solar panel can be defined as the electrical power produced per unit area of the panel. When a solar panel is fixed to the body of a satellite without it being possible to change the angular position of the panel relative to the body of the satellite, the efficiency per unit area depends directly on the angular position of the satellite relative to the sun. Since the angular position of the satellite changes as it travels over its orbit, the mean efficiency per unit area over one revolution is quite low.
To increase the mean efficiency per unit area, it has been proposed to mount the solar panel in a hinged manner on the body of the satellite and to angularly position the panel as well as possible relative to the incident solar flux by means of one or more electric motors and of their control electronic circuitry controlled by a processing unit on board the satellite (which unit manages all of the equipment on board the satellite). The angular positioning device operating properly thus depends on the control electronic circuitry and the processing unit on board the satellite operating properly. This is a drawback insofar as failure of any of these elements might cause a drop in the output of electrical energy, and ultimately might cause all of the electrical equipment on the satellite to stop. Another drawback lies in the complexity of the angular positioning device and in the associated risk of breakdown.
It has also been proposed to equip a space vehicle with a heat-sensitive device suitable for generating torque as a function of exposure to solar radiation, and designed to avoid oscillation phenomena (U.S. Pat. No. 3,311,322).
A heat-sensitive device has also been proposed that is actuated by solar radiation and that is suitable for generating torque for angularly positioning solar panels (U.S. Pat. No. 3,635,015).